CN1205435A - Steel liquid directly fixing aluminium sensor - Google Patents

Abstract

A sensor for directly measuring aluminium content in molten steel is made up by use of the auxiliary electrode system of Al2O3 plus Na3AlF6 and features no need of intermediate oxygen sensor, short response time (less than 10 seconds), no influence from temp, and better match between experimental value, theroretic value and chemically analyzed value.

Description

Molten steel direct aluminum determination sensor

The invention belongs to a chemical sensing test technology.

The aluminum content is an important parameter in the steel smelting process. Aluminum has a great influence on the casting process of steel, the surface quality and the properties of steel. Therefore, it is important to quickly and accurately measure the amount of residual aluminum in steel.

At present, the method for rapidly measuring the content of aluminum in molten steel is mainly carried out by an oxygen determination sensor. Because there is a certain restriction relation between the oxygen content in the molten steel and the impurity elements (or alloy elements), under certain smelting conditions, the relation between the fixed oxygen electromotive force and the residual aluminum amount can be found out:

Lg([％Al]×10³) The aluminum content can be calculated by determining the oxygen sensor electromotive force (= a + bE (mv)) (see K.Hagen et al, "Umschau-Technical Review", Stahl and Eisen, 95(1975), 398). In the formula, E is the electromotive force of the oxygen determination sensor, a.b is an empirical constant which changes along with the change of smelting conditions (such as aluminum adding mode, packing, argon protection and the like), which obviously gives practical resultsThe measurement brings about a lot of inconvenience. In addition, when the oxygen activity in the molten steel is less than 1.8 multiplied by 10, the aluminum is fixed by an oxygen fixing sensor^-7In the presence of [ Al]]，[O]The balance relationship is broken, the actual aluminum determination experimental value is obviously inconsistent with the theoretical value, and the oxygen determination sensor is difficult to adopt (see figure 6).

In order to overcome the defects of the existing oxygen determination sensor aluminum determination, the inventor adopts a novel auxiliary electrode system (Al)₂O₃+Na₃AlF₆) The direct fixed aluminum sensor is made. Experiments prove that the sensor achieves the expected satisfactory effect.

FIG. 1 is a schematic cross-sectional view of a direct-fixed aluminum sensor. It is mainly composed of ZrO₂(MgO) solid electrolyte tube, reference electrode (Mo + MoO)₂) And an auxiliary electrode (Al)₂O₃+Na₃AlF₆) The three parts are as follows. Wherein ZrO₂(MgO) expressed in ZrO₂A small amount of MgO is added. As shown in FIG. 1, the assembly is in a solid electrolyte tube [4]]Outer wall of the electrode, the auxiliary electrode [6]being sintered at 950 DEG C]Attached to a substrate in a tube [4]]The inner bottom is provided with (Mo + MoO)₂) As a reference electrode [7]]The tube is filled with Al₂O₃Powder [5]]The upper end of which is sleeved with Al₂O₃Pipe [2]]And high temperature cement [3]Will [4]]And sealing the container. From a reference electrode [7]]Middle leading-out Mo wire [1]And a molybdenum rod (8) in direct contact with the molten steel]Through a metal wire [9]]Is connected with a secondary instrument.

The auxiliary electrode is made of Al₂O₃And Na₃AlF₆The mixture is mixed into paste and is evenly coated on ZrO₂(MgO) tube [4]]The surface is dried and sintered to obtain the product. Al (Al)₂O₃And Na₃AlF₆The component ratio of (A) can be in accordance with Al shown in FIG. 2₂O₃-Na₃AlF₆The system high-temperature phase diagram ensures that the solid Al is obtained in a test temperature range of T = 1823-1873K₂O₃The principle of coexistence with liquid phase equilibrium is selected. The composition determined in this way not only enables the electrolyte to maintain solid Al at the interface with the molten steel₂O₃The presence of the liquid phase also allows the oxygen ion conduction to be unhindered.For experimentsThe expression of the electrochemical cell of the fixed aluminum sensor is as follows: when the sensor is inserted into molten steel, the following equilibrium reaction exists at the interface of the solid electrolyte and the molten steel

[O]=1／2O₂．．．．．．．．1

........ 2. in this case, the reaction is based on the rationale for the physicochemical reaction and

lgk=-lgPO₂-4／3lga_Al．．．．．．．．．．3 ${\mathrm{lga}}_{\mathrm{Al}}=\lg \[\%\mathrm{Al}\]+\underset{i}{\mathrm{\Σ}}{e}_{\mathrm{Al}}^i\[\%i\]\·\·\·\·\·4$ the content of aluminum in the molten steel can be calculated. In the formula a_Al，PO₂Respectively the Henry activity and the oxygen partial pressure of aluminum in a standard state of a 1% by weight solution, K is the equilibrium constant of reaction (2) [% Al]Is the weight percentage content of aluminum dissolved in molten steel, and e is the interaction coefficient of element i to Al. The parameters that can be selected in the calculation are many. The inventors selected the following data from the given literature for calculation. The thermal data used were:

project equation Al (1) = [ Al](1 Wt% solution) △ G^θ(J／mol)=-63118-27．88T (1)1／2O₂=[O](1 Wt% solution) △ G^θ(J／mol)=-117040-2．88T (2) (s) △G^θ(J/mol) = -1679106+ 321.02T (3) coefficient of interaction $e_{\mathrm{Al}}^{\mathrm{Al}}=0.045$ △G^θ(J/mol) = -546744+ 142.83T (4) formula note (1) above see j.f.elliott: "The Chemistry of Electric Furnace proteins", Electric Furnac Proceedings, 32(1974), 62; note (2) see yellow clan, liu qing nation: "solid electrolyte direct oxygen technology", metallurgical industry press, (1993), 112; note (3) refers to Wei and Shou Kun: "thermodynamics of metallurgical process", Shanghai science and technology Press, 1980: note (4) see D.Janke&W.A.Fischer "Thermochemical Date for The Reaction ， and1／2O₂=[O]in Liquid Iron，Arch．Eisenhuettenwes，4b(1975)755。

Wherein wt% is weight percent, s is solid, l is liquid, △ G^θIs the Gibbs standard free energy of reaction, J/mol is Joule/mole, and T is the absolute temperature.

The experiment of the invention is that Al₂O₃In the crucible, 0.5 kg of steel material is filled, the content of aluminum in the molten steel is measured to be 0.005-0.1% under the protection of pure Ar gas through experiments, and a certain amount of high-purity aluminum wire is added to be more than 99.9% for adjustment. After each aluminum adding, the aluminum sensor is inserted to measure the electromotive force by fully stirring. The insertion time is 10-20 seconds, 3-5 aluminum sensors are determined in each composition test, and a common oxygen determination sensor is used for one-time measurement before an analysis sample is takenAnd fixing to compare with a fixed aluminum sensor.

The experimental temperature is controlled by an up-25 type temperature controller, and the precision is +/-1K. The time interval for inserting the fixed aluminum sensor is controlled so that the temperature change caused by inserting the fixed aluminum sensor into the molten steel is within +/-5K. The battery electromotive force of the sensor is recorded by a 3057-22 long-chart recorder with 1M omega internal resistance so as to analyze the response process and take values.

See FIGS. 3-7 for examples of the experiments.

Fig. 3 is a graph of typical fixed aluminum electromotive force versus time. Wherein, the EMF of the longitudinal coordinate is the constant aluminum electromotive force, mv is millivolt, the t of the horizontal coordinate is time, and s is second. Experimental conditions were T =1823K, [% Al]= 0.003. The plateau where the curve occurs around 5 seconds is due to insufficient range of the meter. The experimental result shows that the response speed of the invention is within 10 seconds, and the invention completely meets the requirement of on-site measurement.

Fig. 4 is a comparison of the experimental value (▲) of the logarithmic relationship between electromotive force and aluminum activity with the theoretical calculation value (□) (T = 1823K).

FIG. 5 is a comparison of the experimental values (▲) and theoretical values (□) of the logarithmic relationship between electromotive force and aluminum activity at T = 1823-1873K, and the experimental results show that the agreement between the two values is still better when measured at different temperatures.

FIG. 6 shows the relationship between electromotive force and logarithm of aluminum activity when aluminum is determined by a common oxygen determination sensor, and experiments show that when the oxygen activity in molten steel is less than 1.8 × 10^-7In time, the experimental values clearly do not match the theoretical values.

FIG. 7 is a graph showing the comparison between the measured value and the chemical analysis value (T =1823K) when aluminum is measured by the present invention, in which the ordinate [% Al]cal is the sensor fixed aluminum value and the abscissa [% Al]ana is the chemical analysis value, and the experiment shows that the distribution of the intersection point (■) is close to a 45 DEG straight line, and the two values are well matched.

Claims (1)

1. A molten steel direct aluminum determination sensor comprises:

   a ZrO₂(MgO) solid electrolyte tube [4]]And an auxiliary electrode [6]sintered on the outer wall thereof]，

   b in the tube [4]]The inner bottom is provided with (Mo + MoO)₂) As a reference electrode [7]]，

   c filling the tube with Al₂O₃The powder (5) is mixed with the raw materials,]in the pipe [4]]Is sleeved with Al at the upper part₂O₃Pipe [2]]And high temperature cement [3]]Will [4]]The sealing is carried out, and the sealing is carried out,

   d from a reference electrode [7]]Middle leading-out Mo wire [1]And a molybdenum rod (8) in direct contact with the molten steel]Through a metal wire [9]]Connected with a secondary instrument, characterized in that the auxiliary electrode is made of (Al)₂O₃+Na₃AlF₆) The system is prepared by mixing the components in a ratio which can be determined within the range of the testing temperature to ensure that Al in a solid state₂O₃And liquid Na₃AlF₃Principle of equilibrium coexistence is formed by Al₂O₃-Na₃AlF₆The high temperature phase diagram of the system (see FIG. 2) is selected.

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